I think peace comes in different ways to each person so you have to decide on what's best for yourself. Personally, I would like to have some quiet time and I think Tsukuba is perfect for that (outside of Tokyo though, but day trip is possible). Cycling alongside rolling paddy fields in Tsukuba and the breathtaking view atop Mount Nyotai are very soothing to the soul. Otherwise, if it's just within Tokyo, attending the concert of my favorite j-rock band worked for me too! But then again, I've yet to explore all of Tokyo so I'll be back for more!
View the beautiful sunset at Odaiba beach. I hope you feel better when you see the sun setting into Tokyo Bay.
Or climb up Tokyo Tower, Tokyo Sky Tree, or observation deck in Roppongi Hills.
Tokyo Bay Cruise is also a good way to enjoy beautiful cityscapes.